1. FIELD OF THE INVENTION
This invention relates generally to vinyl chloride plasticizers and more particularly to novel low volatility plasticizers.
2. DESCRIPTION OF THE PRIOR ART
Many polymeric materials, e.g., poly(vinylchloride), cellulosics, etc., are of a relatively hard and brittle nature. To improve softness and flexibility, so that the resulting product is usable in a wide variety of applications, it is necessary to add a plasticizing agent to the polymer. The basic attributes of a good plasticizer are:
(1) compatibility with the polymer or resin it is to plasticize; PA1 (2) capability of imparting desired processability and softness, etc.; PA1 (3) thermal stability under the conditions of processing and subsequent aging; and PA1 (4) Permanence to loss, particularly through volatilization, but also through solvent extraction, migration or exudation.
Compatibility is normally defined as the ability of the plasticizer to produce a clear film and to remain more or less homogeneously dispersed throughout the resin composition, particularly on aging. Permanence refers to the tendency of the plasticizer to resist loss through volatilization, chemical breakdown, extraction by water, soapy water, or organic solvents, migration and exudation. Other important attributes of a plasticizer are efficiency, i.e., the amount of plasticizer required to impart desired properties (depending on relative costs and specific gravities of the plasticizer and resin, high efficiency can result in reduced or increased volume costs of the plasticized resin composition), ability to impart low temperature flexibility to a resin, ability to allow ease of processing to the resin system, i.e., flows and molds or extrudes readily and the like.
U.S. Pat. No. 4,334,080 relates to a process for preparation of benzenecarboxylic acid esters by reacting benzenecarboxylic acids having 8-10 carbon atoms, or the corresponding carboxylic acid anhydrides, in the presence of amorphous aluminum compound as a catalyst and an alkali metal compound as a promoter; with an aliphatic alcohol having 7-11 carbon atoms, including 2-ethylhexanol, n-octanol, and a variety of straight chain alcohol mixtures (7 to 9, 9 to 10 and 9 to 11 carbon atoms mixtures).
U.S. Pat. No. 3,296,298 relates to polyvinyl chloride compositions plasticized with tetraalkyl pyromellitates in which the alkyl group contains from 6 to 8 carbon atoms, and with pyromellitic esters of branched 6, 7 or 8 carbon-containing alkanol mixtures. Tetraalkyl pyromellitates in which the alkyl groups exceed 8 carbon atoms are said to be of no practical value in polyvinyl resins because they are totally inefficient and fail to impart low temperature flexibility, thereby leading to products which are excessively brittle at low temperature.
Flow promoters for records are disclosed in U.S. Pat. No. 3,280,063 comprising C.sub.10 to C.sub.20 alkyl esters of mono-nuclear aromatic acid of 3 to 6 carboxylic groups, which are employed in amounts of from about 0.05 to 10 parts per 100 parts of total record composition.
Canadian Pat. No. 901,709 relates to vinyl halide resin compositions comprising 100 parts by weight of a vinyl halide resin, 1-2 parts by weight of triallyl cyanurate, 0.5 to 5 parts by weight of an organic peroxide, and 10 to 100 parts by weight of an alkyl pyromellitate ester having 4 to 10 carbon atoms in the ester group. However, only dibutyl-di-(2-ethyl-hexyl)pyromellitate was tested.
Tetra-(2-ethylhexyl)pyromellitate and tetra-(iso-octyl)pyromellitate are known to exhibit moderate exudation in compatability testing, and tetra-decyl pyromellitate is also said to exude. J. R. Darby, Polymer Engineering & Science, 295, 300 (October 1967).
J. Nanu, et al., Materiale Plastice, 12(2), 138-142 (1975) disclose the synthesis and evaluation of n-butyl, neo-butyl, n-pentyl, iso-pentyl, n-hexyl, n-heptyl, n-octyl, iso-octyl and 2-ethylhexyl pyromellitate esters as plasticizers for polyvinyl chloride.
A. DiCio et al., La Chimica E L'Industria, v. 56, 8-12 (1974) relates to the Alusuisse process for manufacture of high purity pyromellitic anhydride, which the authors indicate can be used in the preparation of esters of C.sub.6 -C.sub.14 alcohols, which can be employed in the plasticization of PVC. Such esters are said to have the features of volatility, high heat stability, excellent plasticizing ability even at low temperatures, outstanding dielectric properties and no tendency to migrate. However, no example of the preparation of such esters or their attempted use as plasticizers is given, and the broad utility statement refuted by the weight of the above other prior art teachings for higher alcohol pyromellitic esters.